The use of gear boxes to provide four output speeds in a single direction of rotation from a two-speed reversible drive input has been known in the commercial appliance art. Generally, most prior art gear boxes provide for one direct drive path from a drive shaft to an output shaft and one alternate drive path from a drive shaft to an auxiliary shaft to an output shaft. Generally, two rotational speeds are provided by the two forward speeds of the motor driving through the drive shaft to the output shaft and two additional speeds are provided by the two reverse speeds of the motor driving through the drive shaft and auxiliary shaft to the output shaft. This system provides for the desired four output speeds. However, such a system has drawbacks.
First, since the drive shaft directly drives the output shaft in one motor direction, any desired speed reduction or increase between the drive shaft and output shaft must be accomplished by a single gear pair. Thus, if a substantial reduction or increase is desired, a very large gear must be present on one of the two shafts, a design element which may be limited by the physical dimensions of the gear box. Additionally, since there is typically only a single gear pair in one drive path the flexibility to design various overall gear ratios through that drive path is extremely limited.
A second major drawback to such prior art drive systems is that the prior art design necessitates that all three shafts be parallel and thus, in a typical arrangement these shafts and the motor are provided in a vertical position. This vertical positioning results in a tall arrangement which requires considerable head room, a limiting factor when the placement of a commercial appliance in a crowded kitchen or manufacturing facility is necessary.
A third drawback of the prior art devices is that in the typical arrangement, the engagement of the drive shaft with either the output or auxiliary shafts induces a radial force on the drive shaft which tends to displace the drive away from the shaft it is driving. Therefore, the shafts and their supporting structures must be sufficiently strong to overcome this radial force which increases the costs of manufacturing and operating such a design.
A further drawback of such prior art designs is that they necessitate the placement of some type of clutch assembly on the drive shaft so that the drive shaft will drive the output shaft when rotated in one direction but will drive the auxiliary shaft when rotation is reversed. Typically, clutches are parts which are subject to increased wear and reduced lifespan and must occasionally be replaced. The placement of such a component on the drive shaft makes its replacement more difficult as the drive shaft is connected to the motor. In fact, servicing a clutch disposed on a drive shaft may necessitate removal of the motor as well as the shaft itself. In such prior art devices, if the clutch is relocated from the drive shaft, it must be placed on the output shaft which is frequently connected to other gearboxes or devices thus making removal of the output shaft as problematic as removal of the drive shaft.
Thus, it is an object of the present invention to provide a four-speed gearbox having multiple unidirectional output speeds based upon a reversible input.
It is a further object of the present invention to provide a four-speed gear box which will provide increased flexibility in the selection of initial, intermediate and final drive ratios.
It is an additional object of the present invention to provide a gearbox which reduces the vertical profile of an appliance utilizing the present gearbox designs and to provide a compact gear-box design without reducing the flexibility in selecting gear ratios for the drive paths.
It is a further object of the present invention to provide a four-speed gearbox which reduces the need for a strengthened, or heavier, drive shaft and supporting structure as a result of radial force on the shaft as a result of the engagement of gears in the drive path.
It is a further object of the present invention to provide a simplified gearbox which avoids the placement of clutches on the primary drive or output shafts to facilitate the service or replacement of components which typically have a lifetime shorter than that of the appliance.